When you use only integers in a division, you will get integer division. When you use (at least one) double or float, you will get floating point division (and the answer you want to get).

So you can declare one or both of the variables as float/double
cast one or both of the variables to float/double.
Do not just cast the result of the integer division to double: the division was already performed as integer division, so the numbers behind the decimal are already lost.

from: https://stackoverflow.com/questions/1666407/sql-server-division-returns-zero